Page 2097 - Week 07 - Thursday, 4 June 2015
I ask leave to make a statement in relation to this paper.
MR CORBELL: I have presented to the Assembly the report on the Yerrabi pond fish kill event that occurred in late 2014, as requested by the Standing Committee on Planning, Environment and Territory and Municipal Services. Over a 25-day period, between 20 September and 14 October 2014, a significant number of dead Murray cod were discovered in the Yerrabi pond. After detailed investigations by the Environment and Planning Directorate, in particular the Conservation Research Branch, including testing of samples by experts in Sydney, there is no clear evidence pointing directly to one single cause of the fish kill of the Murray cod such as a pollution spill.
I would like to mention a number of rainfall and weather conditions that occurred leading up to and during the event that may have contributed to this fish kill. Prior to the event there was a three-day rain event that was then coupled with unseasonably warm temperatures that lasted throughout the period in question. I am advised that 35.4 millimetres of rain fell in the week leading up to the event providing an instant supply of new nutrients into the pond, supplying an abundance of food for aquatic plants and algae and potentially resulting in new plant production and bacterial decomposition. Some of this growth is normally visible across the lake as filamentous algae. These algae produce oxygen during the day but also consume it through the night.
This storm coincided with some unseasonably warm temperatures, actually 6.2 degrees above the monthly long-term average, which then introduced the second potential contributing factor as the ability for water to hold oxygen decreases when temperature increases. I am informed that the increase of nutrients and the inability of water to hold oxygen could potentially have reduced the dissolved oxygen levels in the pond, especially during the pre-dawn hours when plants have consumed oxygen throughout the night.
Unfortunately for our local Murray cod it was also cod breeding season. During the breeding season the behaviour of the larger fish is to guard potential nesting sites which are located at the bottom of the lake, parts of the lake which have the least amount of oxygen. Additionally, the fish are more stressed during the breeding season and tend to be sedentary even if conditions deteriorate.
When considering all of these factors, I am advised that it seems a series of unfortunate concurrent events most likely led to the levels of dissolved oxygen within the Yerrabi pond reaching critically low levels for some of our local Murray cod during this time.
Since 14 October last year there has been no further report of dead Murray cod in Yerrabi pond. On a brighter note, I can report that over the last five years the government has provided $15,000 per annum in funding towards native fish stocking in Canberra’s urban lakes and ponds. The Conservation Research Branch in the